1. Field of the Invention
The present invention concerns a magnetic resistance type sensor used in a magnetic recording device, and more specifically concerns a magnetic sensor and thin-film magnetic head utilizing the spin-valve magnetic resistance effect.
2. Background Information
Recently, magnetic resistance (MR) sensors consisting of a spin-valve film with a sandwich structure in which a pair of magnetic layers with a non-magnetic layer sandwiched in between are laminated on the surface of a substrate have been developed in order to reduce the saturation magnetic field and increase the magnetic field sensitivity in magnetic heads used for playback. In a spin-valve film, the magnetization of one magnetic layer (the pinned magnetic layer) is fixed in the direction of height of the element by the exchange-coupling magnetic field with the antiferromagnetic layer adjacent to said pinned magnetic layer, while the magnetization of the other magnetic layer (the free magnetic layer) is generally converted into a single magnetic domain in the direction of the track width of the element by a hard bias process utilizing the magnetic field of a permanent magnet, so that this magnetization can rotate freely in accordance with the external magnetic field.
As the unidirectional isotropic magnetic field created by the antiferromagnetic layer becomes larger, the pin magnetic layer can be more favorably converted into a single magnetic domain. Furthermore, as the magnetization of this layer becomes more thoroughly fixed, the linearity of the magnetic response to external magnetic fields is more reliably maintained, so that the magnetic characteristics of the magnetic sensor are improved. Accordingly, various antiferromagnetic materials have been proposed in the past. FIG. 11 shows the correlation between the MR ratio and the strength in the (111) direction of an antiferromagnetic layer consisting of PtMn in a so-called bottom type spin-valve film in which the antiferromagnetic layer is disposed on the substrate side.
It is known that the characteristics of antiferromagnetic materials vary according to the underlying material. For example, in Japanese Patent Application Kokai No. 8-315326, a magnetic resistance effect head is disclosed in which a crystalline soft magnetic film which has a high resistance and improves the orientation is installed as the underlayer of the magnetic resistance effect film, so that characteristics such as the magnetic resistance variation rate, etc., can be improved. Furthermore, the magnetic resistance sensor described in Japanese Patent Application Kokai No. 8-213238 uses a Ta underlayer in order to obtain a uniform crystal orientation in the magnetic free layer. Moreover, according to Japanese Patent Application Kokai No. 9-16915, the crystallinity of the antiferromagnetic layer can be improved, and the magnetization of the pin layer can be sufficiently fixed so that a linear magnetic resistance variation is obtained, by using a two-layer film consisting of a Ta film and an NiFe alloy film as the underlayer in a spin-valve magnetic resistance type transducer.
Furthermore, by using an NiFeCr or NiCr underlayer on the surface of the substrate, the magnetic resistance sensor described in U.S. Pat. No. 5,731,936 improves the crystalline structure of the magnetic resistance effect film formed on top of this underlayer, and greatly improves the MR ratio. Moreover, in a paper by Ken'ichi Aoshima et al. titled "Investigation of PdPtMn spin-valve film underlayers" (Nippon Oyo Jiki Gakkai-shi [journal of the Japanese Society of Applied Magnetism], Vol. 22, p. 501-504 (1998)), it is reported that a bottom type spin-valve magnetic resistance sensor using an NiFeCr alloy instead of the conventional NiFe alloy as an underlayer between the substrate and a PdPtMn antiferromagnetic layer disposed on the substrate side shows a higher resistivity than the abovementioned NiFe alloy, and that the current shunt loss is reduced and the MR ratio is improved, and furthermore that the (111) orientation of the antiferromagnetic layer is strengthened, so that the exchange-coupling magnetic field H.sub.ua is increased.
The results of measurements performed by the present applicant regarding the actual relationship between the MR ratio and the strength of the (111) orientation of an underlayer consisting of NiFe in a bottom type spin-valve film in which a PtMn antiferromagnetic layer is disposed on the substrate side are shown in FIG. 12. Furthermore, FIG. 13 shows the relationship between the coercive force Hc of the free magnetic layer and the strength of the (111) orientation of the NiFe underlayer in the same spin-valve film.
However, as a result of the presence of Cr, NiFeCr alloys have the property of bonding with oxygen more readily than NiFe alloys. In actuality, therefore, oxygen couples with the NiFeCr in the film formation process, so that the (111) orientation of the underlayer itself deteriorates, and the (111) orientation of the antiferromagnetic layer formed on top of this underlayer is weakened. As a result, a high MR ratio is not always obtained in actuality; furthermore, there is a danger that the coercive force of the free magnetic layer will increase so that the soft magnetic characteristics drop.
Meanwhile, in a so-called top spin-valve structure in which the antiferromagnetic layer is disposed on the side away from the substrate, if the (111) orientation of the free magnetic layer is insufficient, the ferromagnetic interaction between the free magnetic layer and the pin magnetic layer increases so that the playback output drops, and magnetic instability results. Furthermore, since the (111) orientation of the respective film layers formed on top of the free magnetic layer is weak, an improvement in the MR ratio cannot be achieved. Accordingly, as in the case of the abovementioned bottom spin-valve structure, the (111) orientation cannot be sufficiently strengthened if an NiFeCr alloy is used as the underlayer of the free magnetic layer.
Furthermore, these problems also occur in so-called synthetic type spin-valve structures in which the pin magnetic layer is constructed from a pair of ferromagnetic films that are antiferromagnetically coupled with a non-magnetic film sandwiched in between, and the antiferromagnetic layer and the ferromagnetic film adjacent to this antiferromagnetic layer are exchange-coupled in the presence of the applied magnetic field.